The most senior civil servants in the country tend to be pragmatic and the union that represents them, the FDA, reflects that. But these are turbulent times for public sector managers and Dave Penman, the new general secretary, is taking over the union at a hugely challenging time.

On 2 July Penman officially takes over from Jonathan Baume, and becomes the voice for thousands of senior public sector staff who, bound by the civil service code of impartiality, rarely speak for themselves.

Senior civil servants have been buffeted by a series of attacks on pretty much every aspect of their working lives. There have been big job cuts, with more to come; pay freezes; changes to pensions; and a civil service reform programme that often feels like a personal attack on those whose job is to implement the government's plans.

Last year, FDA anger at government changes to civil service pensions led to the union taking industrial action for the first time ever, although more recently, the union has, reluctantly, voted to accept the proposals, after negotiations that Baume described as the most difficult of his career. Penman says the vote again highlights his members' pragmatism. "It doesn't mean we are happy about it," he says. In fact, as Penman wrote at the time, there are many aspects of the changes with which members remain extremely unhappy.

With 19,000 or so members, the FDA is a small union, compared to other public sector unions, such as Prospect, which represents about 120,000 managers and professional specialists and which also has a new general secretary, Mike Clancy. But because the FDA represents those who work at the very heart of the government, it has a public profile bigger than its membership."This is a job where you have to be the public face of the union and the voice of the senior civil service. It's about defending the public sector ethos. We have a relatively small number of staff, but face big demands."

One of the challenges for the union is the perception that its members are too detached from the real world, in a Sir Humphrey-like bubble. Nothing could be further from the truth, says Penman. "These are some of the brightest people doing some of the most complex jobs in the country. They are up against big financial constraints and face almost constant reorganisation, on the basis of what many would see as arbitrary decisions. None of that is helped by constant sniping from the government."

Like other unions, the FDA faces falling membership as cuts are made to civil service jobs. Hard times have resulted in a growing recognition of the importance of a collective approach, and Penman says the FDA has a good reach across senior civil service grades - he's particularly proud of the fact that a third of the union's members are government lawyers - but it's becoming harder for all unions to make the books balance.

At its recent annual general meeting, the union voted to increase subscriptions. "As a small union, it can be difficult to maintain that viability," acknowledges Penman. "But we need a greater contingency fund for those big legal cases. It's very difficult when our members face a pay freeze." One such case was that of Brodie Clark, the former head of the Border Force, who controversially resigned last November and who reached an out-of-court settlement with the Home Office in March.

Representing the top echelons of Whitehall was not originally on the radar of a boy from a working class Glasgow family. "I never thought I would end up as FDA general secretary," says Penman. "As I've worked my way up, I've thought about top jobs, but I'm not from the usual background."

Penman's commitment to union activism began early. He was on a picket line, aged 14, when his mother, also a civil servant, went on strike in 1981. When he then became a civil servant himself, being involved in the union not only seemed to be the natural thing to do. Penman has been a full-time union official since 1995 and has worked for the FDA since 2000.

He now becomes the organisation's fifth general secretary and acknowledges that both his predecessors in the role – Jonathan Baume, general secretary since 1997, and Liz, now Baroness, Symons, general secretary from 1989-1997 – are hard acts to follow.

Whitehall is continually exhorted to be more entrepreneurial, more focused on performance management. In May, cabinet secretary Sir Jeremy Heywood warned that more than 40,000 civil servants deemed to be performing poorly might face losing their jobs. The government's plans for civil service reform are due to be published in white paper form soon, but Penman believes the white paper will be less dramatic than has been trailed and points out that there has already been a lot of work on issues such as increasing the skills and capabilities of departments, and introducing more performance management of civil servants.

"It might be quite challenging, but I'm quite sceptical," he says. Pragmatism and scepticism are notable virtues of the civil service; it sounds as though their new union leader is already well in tune with his members.